Structural Reliability Analysis (SRA) is a tool for calculating failure probabilities of a structure that takes
into account all random variables involved in ship structural design and provides a better and
alternative to deterministic approaches. With a number of different regulations based on structural
reliability theory already existing for some time now in the areas of Civil and Aeronautical engineering
and the Nuclear Power industry it has been only a matter of time before the ship/offshore field
implemented such a procedure into its regulatory regime. Classification Societies have published since
the early 1990s suggestions of how reliability analysis techniques can be used to analyse structures
and recently some have incorporated and accepted those as an equivalent means of analyzing
structures to supplement their existing regulations.

This research examines the structural reliability of Floating Production, Storage and Offloading
Vessels (FSPSO)/Tanker structures already in operation in the North Sea/West of Shetland area,
using a component time-variant reliability approach that takes into account the most suitable approach
for calculating the ultimate strength of the vessel’s structure. Corrosion effects on the structure are
modelled using a non-linear mathematical model based on actual measurements. Emphasis is placed
on the modelling of loads for use in reliability analysis. Load combination methodology is used for the
combination of wave bending, still water, slamming and thermal loads using a variety of different
approaches. FPSO/Tanker vessels are analysed using First and Second Order Reliability Method
(FORM/SORM) but also time-variant Monte Carlo simulation component reliability techniques to obtain
Partial Safety Factors and probabilities of failure.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its
contents, including any opinions and/or conclusions expressed, are those of the authors alone and
do not necessarily reflect HSE policy.